The invention relates to an apparatus for measuring the contents of foreign matters in a fluid, in particular a buoyant apparatus, with a housing of thermoplastic synthetic material and a hole in a first wall section and a through-hole in a second wall section, whereby a sensor for the foreign matter is arranged in the housing and projects in the hole, and whose outer surface tightly closes the hole with the outer side of the first wall section, the sensor, in an area around the hole, being permeable to the foreign matters that are to be measured, and two parts of the housing being joined materially in an area of their edge sections.
An apparatus of this kind is known from GB 2 005 421 A. It serves to analyse wastewater, in particular for the measurement of the oxygen content. Besides, it can be used to measure nutrient solutes in the water, e.g. nitrates and phosphates. The housing is a buoyant hollow ball. The sensor has on its outer side a diaphragm, through which the foreign matter that is to be measured can diffuse. This diaphragm closes the hole, in which the sensor is arranged, tightly with the outer side of the housing. The ball-shaped form of the housing gives the advantage, that it counteracts a contamination of the outer side of the diaphragm, for example fouling or an oil film, when the fluid, that is to be examined, flows. The diaphragm is arched corresponding to the arched shape of the outer surface of the housing, and thereby increases the flow velocity in the area of the diaphragm, in order that contaminations are not easily accumulated there, and therefore will not impair the measuring ability of the sensor. The housing is manufactured in a rotational casting process, whereby the hole in the housing is formed co-axial with the rotating axis. Following this, a through-going inner pipe is adhered to the hole. The sensor has an external screw thread, by means of which it is screwed to an internal thread in one end of a lead-through pipe. Together with the sensor the lead-through pipe is inserted into the adhered inner pipe and fixed to the housing by means of a cap nut.
The manufacturing of this apparatus takes place in several steps and is time-consuming. In particular, the glueing of the housing and the inner pipe increases the manufacturing time due to the required curing time for the adhesive.
Further, in an apparatus of this kind, two halves of the housing has been manufactured in an injection mould process with subsequent bonding by means of ultrasonic welding.
The manufacturing time will hereby be somewhat reduced, however, in both cases two screw connections must not only be manufactured, but also manually handled, both during assembly of the sensor and during replacement of the sensor.
The object of the invention is to achieve an apparatus of the generic art described in the introduction, which is easier to manufacture.
According to the invention this task has been solved in that both of the housing parts comprise on their inner side an inner wall opposite to the edge sections and bridging these, and defining an intermediate space together with the outer wall of the housing, the inner wall being made of two wall parts having edges opposite to the edge portions of the housing parts and abutting one another, and that the intermediate space is filled with a hardened material which is materially joined with the outer wall and the inner wall.
By using this solution the two housing parts can be manufactured in the same mould, for example in an injection mould process. An electronic circuit for the sensor and its connecting wires can be inserted into the one housing part and the two housing parts can be joined together, or alternatively clipped together. The intermediate space that has been formed in this way can be filled via at least one filling opening with the uncured material which after curing materially joins the outer wall and the inner wall, and at the same time seals the edge sections of the two housing parts in the area of the inner and outer wall.
Preferably, the two housing parts contain polybutylenterephetalate. This material exhibits high strength, stiffness, hardness and lov ductility at low temperatures, while showing dimensional stability at high temperatures. Besides, it has a high resistance and stability towards organic dissolvents, oils and grease.
The heated filling material can be melted together with a corresponding thermoplastic synthetic material of the housing. Preferably though, the material that is filled into the intermediate space is glued together with the synthetic material of the housing.
If the material filled into the intermediate space contains polyurethane, it cannot only be glued easily together with polybutylenterephtalate, but it can also quickly be cured, so that the duration of curing will be short.
In the housing a printed circuit board for the sensor can be arranged and, through at least one sealable opening in the inner wall be encapsulated with the same material as the intermediate space. The filling of the intermediate space and the encapsulation of the printed circuit board can take place in directly successive manufacturing steps, whereby at the same time the hole of the housing which contains the sensor is being sealed from the inside.
The first wall section can form a separate part which is detachably connected with the second wall section. By detaching the first wall section from the second wall section, the sensor can be easily and quickly replaced.
In particular, the sensor can be replaced quickly, if the first wall section has a first lead-through connection piece which surrounds the hole, and which by means of a bayonet socket is connected with a second lead-through connection piece of the second wall section.
The wall sections can both be arched towards the outer side, preferably with a spherical shape. In case of a flowing liquid, a rapid flow around the wall sections is generated, whereby the outer side of the sensor which is formed as a diaphragm is prevented from becoming less permeable or completely impermeable due to a contamination of for example fouling or an oil film, which will lead to malfunction of the apparatus.